Despite growing interest in magnetic resonance of porous materials such as soils and concrete, critical limitations exist in terms of the types of measurements that can be made. Both spectroscopic and spatially resolved studies requiring superconducting magnets can only be carried out on samples of limited size. New advances in open, portable NMR instrumentation allow bulk relaxation and diffusion measurements to be made on arbitrarily large samples such as described in G. Eidmann, R. Savelsberg, P. Blümler, B. Blümich, J. Magn. Res. A 1996; 122:104-109. However, experiments of this type are limited by the penetration depth of B0 and B1. This constraint has permitted higher field (10-20 MHz) near surface studies (see Boguszynska, J. et al., Cem. Concr. Res, 2005 35:2033-2040), along with lower field measurements at a greater, but still limited, depth.
In many situations, it may be desirable to measure NMR parameters from deep within a sample. Examples in the porous media regime could include larger concrete structures and soil formations. Previous work has used RF coils embedded within concrete samples in order to alleviate the B1 penetration problem (see Boguszynska, above).
Extending this idea, a small, low cost NMR sensor suitable to be embedded within a large sample has been developed. NdFeB disk magnets provide a local B0 field for a 1H resonant frequency of between 6-10 MHz depending on the design. A printed circuit board surface coil is located immediately above one face of the magnets, and tuned to resonance with capacitors on the opposite face. The entire arrangement is connected to a 2.5 mm diameter coaxial cable, and encased in epoxy. The inhomogeneous B0 and B1 fields define a local sensitive spot in which bulk relaxation time or diffusion measurements can be made.
According to one aspect of the present invention, there is provided a probe suitable for use in unilateral nuclear magnetic resonance imaging and adapted to be embedded in a sample to be analysed, the probe comprising; a magnet having a north and south pole; a radiofrequency coil adjacent one of the poles of the magnet; a capacitive tuning circuit adjacent the other pole of the magnet; a coaxial cable electrically connected to the tuning circuit and the tuning circuit electrically connected to the coil.
According to another aspect of the present invention, there is provided a probe suitable for use in unilateral nuclear magnetic resonance imaging and adapted to be embedded in a sample to be analysed, the probe comprising; a static magnetic field generator; a radiofrequency magnetic field generator adjacent to the static magnetic field generator; a circuit controlling the frequency response of the radiofrequency magnetic field generator, adjacent to the static magnetic field generator; an input cable coupled to the frequency control circuit and the frequency control circuit coupled to the radiofrequency magnetic field generator.
According to another aspect of the present invention, there is provided a method for magnetic resonance imaging of a sample comprising the step of embedding a probe in the sample to be imaged.
According to another aspect of the present invention, there is provided a system for use in unilateral nuclear magnetic resonance imaging comprising: a probe adapted to be embedded in a sample to be analysed, an RF supply module connected to probe suitable for generating an RF signal compatible with nuclear magnetic resonance.
An RF coil suitable for nuclear magnetic resonance imaging wherein the coil in bowtie shaped. The coil may have multiple windings.
Other aspects and features of the present invention will become apparent to those ordinarily skilled in the art upon review of the following description of specific embodiments of a probe, system and method suitable for unilateral nuclear magnetic resonance in conjunction with the accompanying drawing figures.
Like reference numerals are used in different figures to denote similar elements.